This proposal seeks to provide an understanding of the interaction between RNA Polymerase of Bacillus subtilis and specific bases in the promoter region. The object is to discover the roles of various sub-regions of the promoter and of various subunits of RNA polymerase in the different steps in transcription (i.e., initial binding, formation of complexes that are competent to initiate transcription, synthesis of the first phosphodiester bond, elongation). This will be approached by creating mutations in selected sites within the promoter and asking which step in transcription is affected by each mutation. Mutations in RNA polymerase will also be sought, particularly mutations that compensate for a defect in promoter structure. In addition, the expression of heterologous promoters in B. subtilis will be examined. This will provide clues as to which aspects of promoter structure are most important and help identify reasons why certain genes are expressed in some hosts but not in others.